The present invention relates to pistons for compressors and methods and apparatuses for coating the compressor pistons.
A typical piston type compressor employed in an air-conditioning system includes a housing and a drive shaft, which is supported in the housing. A swash plate is fixed to the drive shaft and supported so as to rotate integrally with the shaft. The housing includes a cylinder block. The cylinder block is provided with cylinder bores. Each cylinder bore accommodates a piston. The piston is coupled to a swash plate by means of shoes. A compression chamber is defined in each cylinder bore by the associated piston. The integral rotation of the drive shaft and the swash plate reciprocates the pistons. The reciprocation of each piston alters the volume of the associated compression chamber and causes compression of the refrigerant gas drawn into the compression chamber.
A typical piston is substantially cylindrical. The outer surface of the piston contacts the wall of the associated cylinder bore. With such a piston, it is required that the space between the piston and the wall of the associated bore be sealed. Furthermore, it is required that the piston and the wall of the cylinder bore have an anti-abrasion property.
The outer surface of the piston is coated by a material, the main component of which is polytetrafluoroethylene (PTFE) or the like to improve the sealing and anti-abrasion properties of the piston. The coating material is sprayed onto the piston.
However, spray coating has the following disadvantages:
(1) In addition to portions that require application of the coating, portions that do not require sealing and anti-abrasion properties are also coated. Furthermore, some of the coating material is dispersed around the piston and is wasted.
(2) Each piston is provided with a seat to receive the associated shoe. Since a clearance having a predetermined dimension must accurately be provided between the shoe and the shoe seat, it is preferable that the shoe not be coated. Application of a coating to the shoe seat changes the clearance dimension. Thus, the shoe seat is masked to prevent application of the coating. The masking process and the masking removal process increases the number of steps required during coating of the piston.
(3) Peripheral equipment such as a protection fence must be arranged in the room in which the coating process is carried out to prevent the coating from being widely dispersed. Furthermore, the coating sprayed onto such peripheral equipment must be cleaned periodically.
For the reasons described above, the application of a coating to the piston, increases costs. This leads to an increase in the price of the compressor.